Plasmonic Probe With Circular Nano-Moat for far-Field Free Nanofocusing.

In this work, a metallic probe with a sharp tip and two half-circular nanostructures on its base is introduced and investigated. The proposed design aims at improving the detection performance of a probe for scattering scanning near-field optical microscopy in terms of enhanced signal-to-noise ratio. Under the premise of processing feasibility, the structure of the probe is designed and optimized with three-dimensional finite-difference time-domain method. And then the performance and optical property of the probe are theoretically investigated and experimentally demonstrated using a scanning near-field optical microscope with aperture probe. It is indicated that a tightly confined optical field with significantly reduced far-field background can be achieved at the tip apex of the probe.